1. Field of the Invention
The invention relates to ceramic material suitable for use in production of paving tiles, construction tiles, flooring in offices, flooring in machinery plants and so forth, and more particularly, to a ceramic material obtained by a method comprising steps of mixing defatted bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture thus obtained to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture after the primary firing into carbonized powders, kneading the carbonized powders with which ceramic powders, a solvent, and a binder as desired are mixed into a plastic workpiece (kneaded mass), pressure-forming the plastic workpiece at pressure in a range of 10 to 100 MPa, and subjecting a formed plastic workpiece thus obtained again to firing in an inert gas atmosphere at a temperature in a range of 100 to 1400xc2x0 C.
2. Description of the Related Art
In the past, porcelain clay, feldspathic clay, and silica-alumina based ceramic powders have been in widespread use for production of paving tiles, and construction tiles. Synthetic resin as represented by vinyl chloride has been in use for flooring in offices and machinery plants. However, conventional tiles have been slippery because of the hard surface thereof while flooring in offices, made of synthetic resin, have had insulating property, and been prone to generation of static electricity, so that there have been involved risks of the flooring not only giving discomfort but also causing the erroneous operation of a computer and the like. In addition, there has been a possibility of oil dropping on the floor in plants such as a machinery plant, causing workers to slip and fall on the floor. This has posed operational problems.
Meanwhile, an attempt to obtain a porous carbonaceous material by utilizing rice bran, produced in quantity of 900,000 tons a year in Japan and in as much as 33 million tons a year throughout the world, has been well known by researches carried out by Mr. Kazuo Hokkirigawa, the first inventor of the present invention (refer to xe2x80x9cFunctional Materialxe2x80x9d, May issue, 1997, Vol. 17, No. 5, pp. 24xcx9c28).
Herein are disclosed a carbonaceous material obtained by mixing defatted bran derived from rice bran with a thermosetting resin before kneading, drying a formed kneaded mixture obtained by pressure-forming a kneaded mixture, and subsequently, firing the formed kneaded mixture as dried in an inert gas, and a method of producing the carbonaceous material.
With such a method as described above, however, it has been practically difficult to form the formed kneaded mixture with precision because there occurs discrepancy in dimensions by as much as 25% in terms of a contraction ratio of the dimensions of the formed kneaded mixture prepared by the step of pressure-forming to those of a finished formed product obtained after the step of firing in the inert gas.
It is therefore an object of the invention to provide a ceramic material having such properties as a small contraction ratio of the dimensions of a formed ceramic workpiece to those of a finished product, excellent electric conductivity, small thermal strain, insusceptibility to damage, tendency of an increase in friction resistance when wet, light weight, a long service life, and ability to absorb oil and grease with ease, providing at the same time a high-tech eco-material (state-of-the-art material excellent in ecological adaptability) capable of utilizing biomass resources, which is different from the conventional industrial material.
The inventor of the present invention has found out that the ceramic material having the properties as described above can be obtained, and succeeded in development of the invention. That is, there has been developed a ceramic material having excellent properties required of ceramic material, including a small contraction ratio in the dimensions of a formed ceramic workpiece to those of a finished product, suitable for use in production of paving tiles, construction tiles, flooring in offices, flooring in machinery plants and so forth.
The inventor of the present invention has conducted intense studies, and found out that a ceramic material is obtained by a method comprising steps of mixing defatted bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture thus obtained to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture after the primary firing into carbonized powders, kneading the carbonized powders with which ceramic powders, a solvent, and a binder as desired are mixed into a plastic workpiece (kneaded mass), pressure-forming the plastic workpiece at pressure in a range of 10 to 100 NPa, and subjecting a formed plastic workpiece thus obtained again to firing in an inert gas atmosphere at a temperature in a range of 100 to 1400xc2x0 C.
More specifically, it has been possible to obtain the ceramic material described above having high compressive strength, a small contraction ratio of the dimensions of a formed ceramic workpiece to those of a finished product, which is 3% or less, 13 wt % of oil absorption ratio, low volume resistivity, and low density with Vickers hardness not less than 300 to 600.
Defatted bran derived from rice bran, used in carrying out the present invention, may be of either local origin or foreign origin regardless of the kind of rice.
Further, any thermosetting resin may be used as long as it has thermosetting property, and typical examples thereof include phenol resin, diaryl phthalate resin, unsaturated polyester resin, epoxy resin, polyimide resin, and triazine resin. In particular, phenol resin is preferably used.
Furthermore, a thermoplastic resin such as a polyamide, and so forth can be used in combination with a thermosetting resin provided that it is used without departing from the spirit and scope of the invention.
Ceramic powders to be mixed with carbonized powders in carrying out the invention are composed of any selected from the group consisting of SiO2, Si3N4, ZrO2, Al2O3, SiC, BN, WC, TiC, Sialon (Sixe2x80x94Alxe2x80x94Oxe2x80x94N based compound solid solution), porcelain clay, feldspathic clay, kaolinite, and so forth.
In the present invention, one kind or not less than two kinds of such ceramic powders as described above may be used.
Ceramic powders not more than 50 xcexcm in grain size are desirable, and those not more than 20 xcexcm in grain size are preferable, those in a range of 0.3 to 3 xcexcm in grain size being more preferably used.
Ceramic powder material as desired can be obtained by mixing the carbonized powders with the ceramic powders not more than 50 xcexcm in grain size.
The carbonized powders can be well mixed with the ceramic powders at a ratio of 5 to 95:95 to 5 by weight.
A mixing ratio of the defatted bran to a thermosetting resin is 50 to 90:50 to 10 by weight, however, the mixing ratio of 75:25 is preferably adopted.
A thermosetting resin in a liquid state, having a relatively small molecular weight, is desirable for use in this case.
A primary firing is performed at a temperature in a range of 700 to 1000xc2x0 C., using normally a rotary kiln, and a firing time is for a duration in a range of 40 to 120 min.
The carbonized powders after the primary firing can be mixed with the ceramic powders at a mixing ratio of the former to the latter of 5 to 95:95 to 5 by weight, however, if a ratio of the carbonized powders exceeds 95% by weight, the stability of the surface hardness of a formed ceramic product as obtained deteriorates while if the ratio thereof is not more than 5% by weight, electric conductivity of the formed ceramic product deteriorates.
A binder used in carrying out the present invention is broadly classified into an organic one and an inorganic one.
Examples of the organic binder are paraffin binders such as polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, methyl cellulose, ethyl cellulose and so forth.
Further, examples of a resin binder material among organic binder materials are phenol resin, polyethylene resin, vinyl acetate resin, epoxy resin, melamine resin, styrol resin, plyacetal resin, polyester resin, polypropylene resin, vinyl chloride resin, acrylic resin, polyamide resin, urethane resin and so forth.
Furthermore, examples of a wax binder material among the organic binder materials are paraffin wax, micro-crystalline wax, Fischer Tropsch wax, polyethylene wax, deformed wax, atactic polypropylene.
Examples of an inorganic binder material among inorganic binder materials used in the binder according to the invention include a phosphoric acid based binder material such as phosphoric acid, aluminum phosphate, pyrophosphoric acid, and trypolyphosphoric acid and a silicon based binder material such as soda silicate, kairome clay (a kind of kaolinite clay). Examples of a titanium based binder material include titania sol.
An amount of the binder to be added represents 1 to 50 parts by weight, preferably, 5 to 20 parts by weight against 100 parts by weight of the carbonized powders combined with the ceramic powders.
A solvent is added such that a plastic workpiece having hardness as desired is obtained by mixing the solvent with the carbonized powders, the ceramic powders, and the binder before kneading. An amount of the solvent to be added represents 5 to 20 parts by weight, preferably, 8 to 15 parts by weight against 100 parts by weight of the carbonized powders combined with the ceramic powders.
Examples of the solvents used in the present invention are water, alcohol such as methanol, ethanol, and propanol, ketone such as acetone, and ethyl methyl ketone, ester, toluene, xylene, Cellosolve, and so forth.
The kneaded mixture of the carbonized powders and the thermosetting resin after the primary firing is pressure-formed at a pressure in a range of 10 to 100 MPa, preferably in a range of 25 to 50 MPa. A die used is preferably at a temperature of about 150xc2x0 C.
A heat treatment is performed at a temperature in a range of 100 to 1400xc2x0 C., and heat treatment time is in a range of about 60 to 120 min.
A warming rate up to a firing temperature is required to be relatively moderate up to 500xc2x0 C. In terms of more specific values, the warming rate is in a range of 0.5 to 3xc2x0 C./min, and is preferably 1xc2x0 C./min.
Further, in lowering the temperature of the kneaded mixture after it is baked, a relatively moderate cooling rate is required until reaching 500xc2x0 C. In terms of more specific values, a cooling rate is in a range of 0.5 to 4xc2x0 C./min, and is preferably 1 to 2xc2x0 C. min. Upon the temperature dropping below 500xc2x0 C., the kneaded mixture is left to cool by itself.
Further, an inert gas atmosphere according to the invention means an atmosphere containing no oxygen which is an active gas, referring to a space vacuumized to a degree or a space filled up with an inert gas. Any gas selected from the group consisting of helium, argon, neon, and nitrogen gas may be used in carrying out the present invention, however, nitrogen gas is preferably used.
Now, the embodiments of the invention are summed up as follows:
(1) a ceramic material obtained by a method comprising steps of mixing defatted bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture thus obtained to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture after the primary firing into carbonized powders, kneading the carbonized powders with which ceramic powders, a solvent, and a binder as desired are mixed into a plastic workpiece (kneaded mass), pressure-forming the plastic workpiece at pressure in a range of 10 to 100 MPa, and subjecting a formed plastic workpiece thus obtained again to firing in an inert gas atmosphere at a temperature in a range of 100 to 1400xc2x0 C.
(2) a ceramic material described under item (1) above wherein the ceramic powders are one kind of, or not less than two kinds of ceramic powders composed of any selected from the group consisting of SiO2, Si3N4, ZrO2, Al2O3, SiC, BN, WC, TiC, Sialon (Sixe2x80x94Alxe2x80x94Oxe2x80x94N based compound solid solution), porcelain clay, feldspathic clay, and kaolinite.
(3) a ceramic material described under item (1) or (2) above wherein the thermosetting resin is one kind of, or not less than two kinds of resins selected from the group consisting of phenol resin, diaryl phthalate resin, unsaturated polyester resin, epoxy resin, polyimide resin, and triazine resin;
(4) a ceramic material described under any one of items (1) to (3) above wherein the binder is an organic binder and/or an inorganic binder, and an amount of the binder to be added represents 1 to 50 parts by weight against 100 parts by weight of the carbonized powders combined with the ceramic powders.
(5) a ceramic material described under any one of items (1) to (4) above wherein a mixing ratio of the defatted bran to the thermosetting resin is 50 to 90:50 to 10 by weight.
(6) a ceramic material described under any one of items (1) to (5) above wherein a mixing ratio of the carbonized powders to the ceramic powders is 5 to 95:95 to 5 by weight.
(7) a ceramic material described under any one of items (1) to (6) above wherein a grain size of the carbonized powders is in a range of 10 to 500 xcexcm.
(8) a formed sintered tile, wherein the ceramic material described under any one of items (1) to (7) above is formed in the shape of a square or rectangular sheet.
(9) a formed sintered flooring, wherein the ceramic material described under any one of items (1) to (7) above is formed in the shape of a square or rectangular sheet.